Sir Alex Ferguson has identified Chelsea as the new challenge to Manchester United's hopes of a record 19th league championship, questioning whether a faltering Arsenal side are paying the price for not having enough experience or mental strength.

"Arsenal are the better footballers but Chelsea are the better, stronger team," Ferguson said of the two clubs currently six points behind United with only five games remaining. Looking at the two of them, Chelsea are far more experienced than Arsenal – far more experienced, a strong team, strong experience. That's the difference between the two teams."

That differs with Ferguson's assessment of the title race two months ago when he spoke at length of it being a two-horse race between Arsenal and United. Since then, however, Arsenal have won only one of their last six league matches as well as losing the Carling Cup final, going out of the FA Cup at Old Trafford and being eliminated from the Champions League by Barcelona.

Chelsea have won six of their last seven league matches to move back into second position on goal difference and Ferguson, once again, is more wary of the team from Stamford Bridge.

"Both are six points behind us, both are our challengers. I have that slight preference for Chelsea because their fixture list is a wee bit easier. They were odds-on at one point for the Premier League and then they hit that blip [winning 10 points in 11 league games]. Credit to us because we took advantage of that." Chelsea, he added, "have to come to Old Trafford and that's not going to be easy for them."

United are certainly in a position of strength, with the opportunity to extend their lead to nine points in the early kick-off at home to Everton, winless at Old Trafford since 1992 and on a run of 14 defeats in their 17 subsequent visits. "Looking behind you is not a bad thing to do with our experience," Ferguson said. "You have to recognise who is behind you. You can't become complacent. It's good to know somebody is behind you and, in that sense, we use our experience. If we win against Everton that leaves us with only four games left and a minimum six-point lead. That's the way to look at it. You run out of games eventually."

Ferguson's team selection will be influenced by the fact the first leg of the Champions League semi-final against Schalke is in Germany on Tuesday, which has left him considering whether to rest Rio Ferdinand and Edwin van der Sar, among others. Dimitar Berbatov is doubtful with a slight groin strain and Ferguson is mindful not to underestimate David Moyes's side. "Everton have done exceptionally well considering David has had a mountain of injuries in the last few weeks, without [Tim] Cahill, [Mikel] Arteta, [Louis] Saha, [Marouane] Fellaini but still turning out the results," he said.

"It's amazing what David has done – even last season when [Phil] Jagielka did his cruciate; he had lots of injuries then, too. He still gets them motivated, he's bringing through some young players, he's freshened his team up and done a fantastic job. They are never easy games against Everton because it's a local derby in a way."

Nonetheless, United have dropped only two points at home all season and are on course to go unbeaten at Old Trafford in the league for the first time since 2000. Ferguson described it as a "fantastic" record and the key factor to their position at the top of the league. Away from home, there have been only five league wins, meaning United could conceivably be the first team since Liverpool in 1976-77 to win the league with fewer than eight victories on the road.

The manager also reported an improvement in Darren Fletcher's condition after the virus that has ruled out the midfielder since the 3-1 defeat at Liverpool on 6 March. Fletcher should be available again in 10 days and Ferguson said: "Darren is a very important player to come back. In big games, important games, Darren has excelled over the years because he has the knowledge and discipline to carry out a job, whatever I want him to do. When he does come back, he will go straight into the team."